[RFC/PATCH] of: Mark property::value as const

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem
with properties that have phandles inside them at some offset that we
need to update. I guess the only real solution is to deep copy the
property in that case and then save around some info to free the
duplicated property later on?

 drivers/of/base.c     |  2 +-
 drivers/of/fdt.c      | 12 ++++++------
 drivers/of/resolver.c |  3 +++
 include/linux/of.h    |  2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index fb6bb855714e..8e5f29b814c9 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -1156,7 +1156,7 @@ EXPORT_SYMBOL_GPL(of_property_count_elems_of_size);
  * property data is too small or too large.
  *
  */
-static void *of_find_property_value_of_size(const struct device_node *np,
+static const void *of_find_property_value_of_size(const struct device_node *np,
 			const char *propname, u32 min, u32 max, size_t *len)
 {
 	struct property *prop = of_find_property(np, propname, NULL);

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index c9b5cac03b36..0635ef5dabf3 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -222,7 +222,7 @@ static void populate_properties(const void *blob,
 
 		pp->name   = (char *)pname;
 		pp->length = sz;
-		pp->value  = (__be32 *)val;
+		pp->value  = val;
 		*pprev     = pp;
 		pprev      = &pp->next;
 	}

@@ -232,6 +232,7 @@ static void populate_properties(const void *blob,
 	 */
 	if (!has_name) {
 		const char *p = nodename, *ps = p, *pa = NULL;
+		char *b;
 		int len;
 
 		while (*p) {

@@ -250,13 +251,12 @@ static void populate_properties(const void *blob,
 		if (!dryrun) {
 			pp->name   = "name";
 			pp->length = len;
-			pp->value  = pp + 1;
+			pp->value  = b = (char *)(pp + 1);
 			*pprev     = pp;
 			pprev      = &pp->next;
-			memcpy(pp->value, ps, len - 1);
-			((char *)pp->value)[len - 1] = 0;
-			pr_debug("fixed up name for %s -> %s\n",
-				 nodename, (char *)pp->value);
+			memcpy(b, ps, len - 1);
+			b[len - 1] = 0;
+			pr_debug("fixed up name for %s -> %s\n", nodename, b);
 		}
 	}
 

diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
index 8bf12e904fd2..6d88f8100318 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c

@@ -93,6 +93,7 @@ static void adjust_overlay_phandles(struct device_node *overlay,
 		if (phandle == OF_PHANDLE_ILLEGAL)
 			continue;
 
+		/* This is bad because we cast away const */
 		*(uint32_t *)prop->value = cpu_to_be32(overlay->phandle);
 	}
 

@@ -154,6 +155,7 @@ static int update_usages_of_a_phandle_reference(struct device_node *overlay,
 			goto err_fail;
 		}
 
+		/* This is bad because we cast away const */
 		*(__be32 *)(prop->value + offset) = cpu_to_be32(phandle);
 	}
 

@@ -222,6 +224,7 @@ static int adjust_local_phandle_references(struct device_node *local_fixups,
 
 			phandle = be32_to_cpu(*(__be32 *)(prop->value + off));
 			phandle += phandle_delta;
+			/* This is bad because we cast away const */
 			*(__be32 *)(prop->value + off) = cpu_to_be32(phandle);
 		}
 	}

diff --git a/include/linux/of.h b/include/linux/of.h
index f22d4a83ca07..b0253886ef46 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h

@@ -35,7 +35,7 @@ typedef u32 ihandle;
 struct property {
 	char	*name;
 	int	length;
-	void	*value;
+	const void *value;
 	struct property *next;
 	unsigned long _flags;
 	unsigned int unique_id;

-- 
2.10.0.297.gf6727b0

On Mon, Feb 13, 2017 at 8:50 PM, Stephen Boyd [off-list ref] wrote:

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

This problem exists with or without this patch, right?

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem
with properties that have phandles inside them at some offset that we
need to update. I guess the only real solution is to deep copy the
property in that case and then save around some info to free the
duplicated property later on?

Couldn't we just copy the overlay and free the firmware blob in this
case? That seems easier than trying to selectively copy things. We
keep the base FDT to pass to userspace and we could need that for
overlays, but not ones we load from userspace.

Rob

On 02/13/17 18:50, Stephen Boyd wrote:

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

The resolver should not be over writing anything in the FDT.  I'll
look at what is going on there.

The FDT we expose to user space should be the FDT we booted with,
not something later modified.

-Frank

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem
with properties that have phandles inside them at some offset that we
need to update. I guess the only real solution is to deep copy the
property in that case and then save around some info to free the
duplicated property later on?

 drivers/of/base.c     |  2 +-
 drivers/of/fdt.c      | 12 ++++++------
 drivers/of/resolver.c |  3 +++
 include/linux/of.h    |  2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

< snip >

On 02/23/17 11:54, Frank Rowand wrote:

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

The resolver should not be over writing anything in the FDT.  I'll
look at what is going on there.

The FDT we expose to user space should be the FDT we booted with,
not something later modified.

It seems that /sys/firmware/fdt is not documented.  I'll look into
fixing that.

-Frank

-Frank

quoted

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem
with properties that have phandles inside them at some offset that we
need to update. I guess the only real solution is to deep copy the
property in that case and then save around some info to free the
duplicated property later on?

 drivers/of/base.c     |  2 +-
 drivers/of/fdt.c      | 12 ++++++------
 drivers/of/resolver.c |  3 +++
 include/linux/of.h    |  2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

< snip >

On 02/23/17 11:54, Frank Rowand wrote:

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

The resolver should not be over writing anything in the FDT.  I'll
look at what is going on there.

OK, now that I have looked at the resolver, I see that you meant that
the resolver code is modifying the _overlay_ FDT, not the FDT that
was used at initial boot.  So not what I thought you meant.

I'll reply separately to the original patch email with a more complete
response.

-Frank

The FDT we expose to user space should be the FDT we booted with,
not something later modified.

-Frank

quoted

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem
with properties that have phandles inside them at some offset that we
need to update. I guess the only real solution is to deep copy the
property in that case and then save around some info to free the
duplicated property later on?

 drivers/of/base.c     |  2 +-
 drivers/of/fdt.c      | 12 ++++++------
 drivers/of/resolver.c |  3 +++
 include/linux/of.h    |  2 +-
 4 files changed, 11 insertions(+), 8 deletions(-)

< snip >

On Thu, Feb 23, 2017 at 2:58 PM, Frank Rowand [off-list ref] wrote:

On 02/23/17 11:54, Frank Rowand wrote:

quoted

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

The resolver should not be over writing anything in the FDT.  I'll
look at what is going on there.

The FDT we expose to user space should be the FDT we booted with,
not something later modified.

It seems that /sys/firmware/fdt is not documented.  I'll look into
fixing that.

That's because the "official" interface is /proc/device-tree/ which is
now a symlink. IIRC, it is documented to use /proc/device-tree, not
the sysfs path.

Rob

On 02/13/17 18:50, Stephen Boyd wrote:

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Instead of struct property field value being a pointer into the
FDT, I would rather copy the data to newly allocated memory and
have value be a pointer to that memory.  This is required if we
want to make /sys/firmware/fdt optional, which would allow us to
free the memory containing the initial boot FDT.

I also do not want overlay live subtrees to have any pointers
into the FDT that was used to populate the overlay, so copying
the data solves that problem also.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

Yes, the resolver code needs to adjust phandle values.

I think I can get rid of the resolver modifying the various phandle
values, and instead just modify the phandle value in struct
device_node.  At the same time, I think I can also remove all
instances of the phandle properties ('linux,phandle', 'ibm,phandle',
'phandle') in the live tree.  These properties should not be
accessed directly by any code outside of the device tree framework
since the phandle is located in the struct device_node.  A quick
grep does not show any such accesses of the phandle properties,
but I want to look more closely.

You can see the problem here by loading an overlay dtb into
the kernel via the request firmware helper method (not direct
loading) and then passing that tree to the resolver on an arm64
device. In this case, the firmware data is vmapped with KERNEL_PAGE_RO
and the code crashes when attempting to write to the blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---

I was thinking perhaps it would work to store another __be32 variant
of the phandle in each device node, but then we still have a problem

That would complicate the overlay code.  Once adjustments are done to
the phandle property value, the overlay code does not need to special
case phandle - phandle is just another property.  I am hoping I can
instead modify the resolver code as I described above.

I would prefer not to hide an assignment in the middle of a statement.

 			*pprev     = pp;
 			pprev      = &pp->next;
-			memcpy(pp->value, ps, len - 1);
-			((char *)pp->value)[len - 1] = 0;
-			pr_debug("fixed up name for %s -> %s\n",
-				 nodename, (char *)pp->value);
+			memcpy(b, ps, len - 1);
+			b[len - 1] = 0;
+			pr_debug("fixed up name for %s -> %s\n", nodename, b);

Nit: I would prefer 'value' to 'b'.  'value' would make the pr_debug longer
that 80 characters, which could be resolved by removing 'for ':

                        pr_debug("fixed up name %s -> %s\n", nodename, value);

What is the result when all of the files that touch value are compiled?
Any warnings or errors?

 	struct property *next;
 	unsigned long _flags;
 	unsigned int unique_id;

-Frank

On 02/23/17 14:09, Rob Herring wrote:

On Thu, Feb 23, 2017 at 2:58 PM, Frank Rowand [off-list ref] wrote:

quoted

On 02/23/17 11:54, Frank Rowand wrote:

quoted

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

The resolver should not be over writing anything in the FDT.  I'll
look at what is going on there.

The FDT we expose to user space should be the FDT we booted with,
not something later modified.

It seems that /sys/firmware/fdt is not documented.  I'll look into
fixing that.

That's because the "official" interface is /proc/device-tree/ which is
now a symlink. IIRC, it is documented to use /proc/device-tree, not
the sysfs path.

Rob
.

Documentation/ABI/testing/sysfs-firmware-ofw describes
/sys/firmware/devicetree/* but not /sys/firmware/fdt


It also describes the /proc/device-tree symlink to
/sys/firmware/devicetree/base as the official
stable ABI, as you mentioned.

So it is just fdt that I have not found the documentation
for.

-Frank

On 02/23/17 15:08, Frank Rowand wrote:

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Instead of struct property field value being a pointer into the
FDT, I would rather copy the data to newly allocated memory and
have value be a pointer to that memory.  This is required if we
want to make /sys/firmware/fdt optional, which would allow us to
free the memory containing the initial boot FDT.

I also do not want overlay live subtrees to have any pointers
into the FDT that was used to populate the overlay, so copying
the data solves that problem also.

quoted

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

Yes, the resolver code needs to adjust phandle values.

I think I can get rid of the resolver modifying the various phandle
values, and instead just modify the phandle value in struct
device_node.  At the same time, I think I can also remove all
instances of the phandle properties ('linux,phandle', 'ibm,phandle',
'phandle') in the live tree.  These properties should not be
accessed directly by any code outside of the device tree framework
since the phandle is located in the struct device_node.  A quick
grep does not show any such accesses of the phandle properties,
but I want to look more closely.

If I remove the various phandle properties from the live tree,
the one place I can not inspect for impact is the live tree that
is exposed at /proc/device-tree/  I do not know whether that is
a problem or not.

-Frank

On Thu, Feb 23, 2017 at 5:08 PM, Frank Rowand [off-list ref] wrote:

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Instead of struct property field value being a pointer into the
FDT, I would rather copy the data to newly allocated memory and
have value be a pointer to that memory.  This is required if we
want to make /sys/firmware/fdt optional, which would allow us to
free the memory containing the initial boot FDT.

Making a copy would simplify several things.

I also do not want overlay live subtrees to have any pointers
into the FDT that was used to populate the overlay, so copying
the data solves that problem also.

quoted

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

Yes, the resolver code needs to adjust phandle values.

I think I can get rid of the resolver modifying the various phandle
values, and instead just modify the phandle value in struct
device_node.  At the same time, I think I can also remove all
instances of the phandle properties ('linux,phandle', 'ibm,phandle',
'phandle') in the live tree.  These properties should not be
accessed directly by any code outside of the device tree framework
since the phandle is located in the struct device_node.  A quick
grep does not show any such accesses of the phandle properties,
but I want to look more closely.

Good idea.

BTW, I recently noticed that dtc by default generates both
linux,phandle and phandle properties. I would think the new one has
been around long enough that we can turn off the old one by default
now.

Rob

Hi Stephen,

On 02/23/17 15:08, Frank Rowand wrote:

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Instead of struct property field value being a pointer into the
FDT, I would rather copy the data to newly allocated memory and
have value be a pointer to that memory.  This is required if we
want to make /sys/firmware/fdt optional, which would allow us to
free the memory containing the initial boot FDT.

I also do not want overlay live subtrees to have any pointers
into the FDT that was used to populate the overlay, so copying
the data solves that problem also.

quoted

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

Yes, the resolver code needs to adjust phandle values.

I think I can get rid of the resolver modifying the various phandle
values, and instead just modify the phandle value in struct
device_node.  At the same time, I think I can also remove all
instances of the phandle properties ('linux,phandle', 'ibm,phandle',
'phandle') in the live tree.  These properties should not be
accessed directly by any code outside of the device tree framework
since the phandle is located in the struct device_node.  A quick
grep does not show any such accesses of the phandle properties,
but I want to look more closely.

After reading through a bit of code, I am confident that I can
modify the resolver code to not modify the various phandle
property values.  There are a few tentacles reaching out to
other areas that I will have to fix also.  The biggest task
for me will be to create some good test code.

I'll be unavailable this week, so I'll start on it in about
a week.

-Frank

Quoting Frank Rowand (2017-03-11 22:27:08)

Hi Stephen,

On 02/23/17 15:08, Frank Rowand wrote:

quoted

On 02/13/17 18:50, Stephen Boyd wrote:

quoted

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Instead of struct property field value being a pointer into the
FDT, I would rather copy the data to newly allocated memory and
have value be a pointer to that memory.  This is required if we
want to make /sys/firmware/fdt optional, which would allow us to
free the memory containing the initial boot FDT.

I also do not want overlay live subtrees to have any pointers
into the FDT that was used to populate the overlay, so copying
the data solves that problem also.

quoted

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

Yes, the resolver code needs to adjust phandle values.

I think I can get rid of the resolver modifying the various phandle
values, and instead just modify the phandle value in struct
device_node.  At the same time, I think I can also remove all
instances of the phandle properties ('linux,phandle', 'ibm,phandle',
'phandle') in the live tree.  These properties should not be
accessed directly by any code outside of the device tree framework
since the phandle is located in the struct device_node.  A quick
grep does not show any such accesses of the phandle properties,
but I want to look more closely.

After reading through a bit of code, I am confident that I can
modify the resolver code to not modify the various phandle
property values.  There are a few tentacles reaching out to
other areas that I will have to fix also.  The biggest task
for me will be to create some good test code.

I'll be unavailable this week, so I'll start on it in about
a week.

Ok. No worries from my side. I'm interested to see how random properties
will be "corrected" without modifying them. I can only assume the plan
is to copy those properties.

The kbuild robot found more cases where marking this as const causes
issues. Please see the updated patch inline.

-----8<-----
From: Stephen Boyd <redacted>
Subject: [PATCH] of: Mark property::value as const

The 'blob' we pass into populate_properties() is marked as const,
but we cast that const away when we assign the result of
fdt_getprop_by_offset() to pp->value. Let's mark value as const
instead, so that code can't mistakenly write to the value of the
property that we've so far advertised as const.

Unfortunately, this exposes a problem with the fdt resolver code,
where we overwrite the value member of properties of phandles to
update them with their final value. Add a comment for now to
indicate where we're potentially writing over const data.

You can see such the problem here by loading an overlay dtb into
the kernel via the fw helper method (not direct loading) and
passing that tree to the resolver on an arm64 device. In this
case, the firmware data is vmapped with KERNEL_PAGE_RO and the
resolver code crashes when attempting to write to blob to update
the phandle properties.

Signed-off-by: Stephen Boyd <redacted>
---
 drivers/of/base.c     |  2 +-
 drivers/of/fdt.c      | 12 ++++++------
 drivers/of/pdt.c      |  9 +++++----
 drivers/of/resolver.c |  3 +++
 fs/openpromfs/inode.c |  2 +-
 include/linux/of.h    |  2 +-
 6 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index fb6bb855714e..8e5f29b814c9 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c

@@ -1156,7 +1156,7 @@ EXPORT_SYMBOL_GPL(of_property_count_elems_of_size);
  * property data is too small or too large.
  *
  */
-static void *of_find_property_value_of_size(const struct device_node *np,
+static const void *of_find_property_value_of_size(const struct device_node *np,
 			const char *propname, u32 min, u32 max, size_t *len)
 {
 	struct property *prop = of_find_property(np, propname, NULL);

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index c9b5cac03b36..0635ef5dabf3 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -222,7 +222,7 @@ static void populate_properties(const void *blob,
 
 		pp->name   = (char *)pname;
 		pp->length = sz;
-		pp->value  = (__be32 *)val;
+		pp->value  = val;
 		*pprev     = pp;
 		pprev      = &pp->next;
 	}

@@ -232,6 +232,7 @@ static void populate_properties(const void *blob,
 	 */
 	if (!has_name) {
 		const char *p = nodename, *ps = p, *pa = NULL;
+		char *b;
 		int len;
 
 		while (*p) {

@@ -250,13 +251,12 @@ static void populate_properties(const void *blob,
 		if (!dryrun) {
 			pp->name   = "name";
 			pp->length = len;
-			pp->value  = pp + 1;
+			pp->value  = b = (char *)(pp + 1);
 			*pprev     = pp;
 			pprev      = &pp->next;
-			memcpy(pp->value, ps, len - 1);
-			((char *)pp->value)[len - 1] = 0;
-			pr_debug("fixed up name for %s -> %s\n",
-				 nodename, (char *)pp->value);
+			memcpy(b, ps, len - 1);
+			b[len - 1] = 0;
+			pr_debug("fixed up name for %s -> %s\n", nodename, b);
 		}
 	}
 

diff --git a/drivers/of/pdt.c b/drivers/of/pdt.c
index d2acae825af9..6984717fcfb7 100644
--- a/drivers/of/pdt.c
+++ b/drivers/of/pdt.c

@@ -94,6 +94,7 @@ static struct property * __init of_pdt_build_one_prop(phandle node, char *prev,
 {
 	static struct property *tmp = NULL;
 	struct property *p;
+	char *s;
 	int err;
 
 	if (tmp) {

@@ -109,8 +110,8 @@ static struct property * __init of_pdt_build_one_prop(phandle node, char *prev,
 	if (special_name) {
 		strcpy(p->name, special_name);
 		p->length = special_len;
-		p->value = prom_early_alloc(special_len);
-		memcpy(p->value, special_val, special_len);
+		p->value = s = prom_early_alloc(special_len);
+		memcpy(s, special_val, special_len);
 	} else {
 		err = of_pdt_prom_ops->nextprop(node, prev, p->name);
 		if (err) {

@@ -123,12 +124,12 @@ static struct property * __init of_pdt_build_one_prop(phandle node, char *prev,
 		} else {
 			int len;
 
-			p->value = prom_early_alloc(p->length + 1);
+			p->value = s = prom_early_alloc(p->length + 1);
 			len = of_pdt_prom_ops->getproperty(node, p->name,
 					p->value, p->length);
 			if (len <= 0)
 				p->length = 0;
-			((unsigned char *)p->value)[p->length] = '\0';
+			s[p->length] = '\0';
 		}
 	}
 	return p;

diff --git a/drivers/of/resolver.c b/drivers/of/resolver.c
index 8bf12e904fd2..6d88f8100318 100644
--- a/drivers/of/resolver.c
+++ b/drivers/of/resolver.c

@@ -93,6 +93,7 @@ static void adjust_overlay_phandles(struct device_node *overlay,
 		if (phandle == OF_PHANDLE_ILLEGAL)
 			continue;
 
+		/* This is bad because we cast away const */
 		*(uint32_t *)prop->value = cpu_to_be32(overlay->phandle);
 	}
 

@@ -154,6 +155,7 @@ static int update_usages_of_a_phandle_reference(struct device_node *overlay,
 			goto err_fail;
 		}
 
+		/* This is bad because we cast away const */
 		*(__be32 *)(prop->value + offset) = cpu_to_be32(phandle);
 	}
 

@@ -222,6 +224,7 @@ static int adjust_local_phandle_references(struct device_node *local_fixups,
 
 			phandle = be32_to_cpu(*(__be32 *)(prop->value + off));
 			phandle += phandle_delta;
+			/* This is bad because we cast away const */
 			*(__be32 *)(prop->value + off) = cpu_to_be32(phandle);
 		}
 	}

diff --git a/fs/openpromfs/inode.c b/fs/openpromfs/inode.c
index 13215f26e321..68cbb3fddbc2 100644
--- a/fs/openpromfs/inode.c
+++ b/fs/openpromfs/inode.c

@@ -65,7 +65,7 @@ static int is_string(unsigned char *p, int len)
 static int property_show(struct seq_file *f, void *v)
 {
 	struct property *prop = f->private;
-	void *pval;
+	const void *pval;
 	int len;
 
 	len = prop->length;

diff --git a/include/linux/of.h b/include/linux/of.h
index f22d4a83ca07..b0253886ef46 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h

@@ -35,7 +35,7 @@ typedef u32 ihandle;
 struct property {
 	char	*name;
 	int	length;
-	void	*value;
+	const void *value;
 	struct property *next;
 	unsigned long _flags;
 	unsigned int unique_id;

-- 
2.10.0.297.gf6727b0

Hi Stephen,

[auto build test WARNING on linus/master]
[also build test WARNING on v4.11-rc2 next-20170310]
[cannot apply to glikely/devicetree/next]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Stephen-Boyd/of-Mark-property-value-as-const/20170317-143414
config: sparc64-allmodconfig (attached as .config)
compiler: sparc64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=sparc64 

All warnings (new ones prefixed by >>):

   fs/openpromfs/inode.c: In function 'property_show':

quoted

fs/openpromfs/inode.c:74:16: warning: passing argument 1 of 'is_string' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]

     if (is_string(pval, len)) {
                   ^~~~
   fs/openpromfs/inode.c:48:12: note: expected 'unsigned char *' but argument is of type 'const void *'
    static int is_string(unsigned char *p, int len)
               ^~~~~~~~~

vim +74 fs/openpromfs/inode.c

^1da177e Linus Torvalds  2005-04-16  58  
3d824a46 David S. Miller 2006-06-25  59  		return 0;
^1da177e Linus Torvalds  2005-04-16  60  	}
^1da177e Linus Torvalds  2005-04-16  61  
3d824a46 David S. Miller 2006-06-25  62  	return 1;
3d824a46 David S. Miller 2006-06-25  63  }
^1da177e Linus Torvalds  2005-04-16  64  
3d824a46 David S. Miller 2006-06-25  65  static int property_show(struct seq_file *f, void *v)
3d824a46 David S. Miller 2006-06-25  66  {
3d824a46 David S. Miller 2006-06-25  67  	struct property *prop = f->private;
755d4871 Stephen Boyd    2017-03-14  68  	const void *pval;
3d824a46 David S. Miller 2006-06-25  69  	int len;
^1da177e Linus Torvalds  2005-04-16  70  
3d824a46 David S. Miller 2006-06-25  71  	len = prop->length;
3d824a46 David S. Miller 2006-06-25  72  	pval = prop->value;
^1da177e Linus Torvalds  2005-04-16  73  
3d824a46 David S. Miller 2006-06-25 @74  	if (is_string(pval, len)) {
3d824a46 David S. Miller 2006-06-25  75  		while (len > 0) {
3d824a46 David S. Miller 2006-06-25  76  			int n = strlen(pval);
^1da177e Linus Torvalds  2005-04-16  77  
3d824a46 David S. Miller 2006-06-25  78  			seq_printf(f, "%s", (char *) pval);
^1da177e Linus Torvalds  2005-04-16  79  
3d824a46 David S. Miller 2006-06-25  80  			/* Skip over the NULL byte too.  */
3d824a46 David S. Miller 2006-06-25  81  			pval += n + 1;
3d824a46 David S. Miller 2006-06-25  82  			len -= n + 1;

:::::: The code at line 74 was first introduced by commit
:::::: 3d824a46b7210ea3b0a13ab0d0fbd7f6e2e91ddf [OPENPROMFS]: Rewrite using in-kernel device tree and seq_file.

:::::: TO: David S. Miller [off-list ref]
:::::: CC: David S. Miller [off-list ref]

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
-------------- next part --------------
A non-text attachment was scrubbed...
Name: .config.gz
Type: application/gzip
Size: 49518 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20170317/0ec05757/attachment-0001.gz>

Hi Stephen,

[auto build test ERROR on linus/master]
[also build test ERROR on v4.11-rc2 next-20170310]
[cannot apply to glikely/devicetree/next]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Stephen-Boyd/of-Mark-property-value-as-const/20170317-143414
config: powerpc-allnoconfig (attached as .config)
compiler: powerpc-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        make.cross ARCH=powerpc 

All errors (new ones prefixed by >>):

   arch/powerpc/kernel/pci_32.c: In function 'pcibios_make_OF_bus_map':

quoted

arch/powerpc/kernel/pci_32.c:141:10: error: passing argument 1 of 'memcpy' discards 'const' qualifier from pointer target type [-Werror=discarded-qualifiers]

      memcpy(map_prop->value, pci_to_OF_bus_map, pci_bus_count);
             ^~~~~~~~
   In file included from include/linux/string.h:18:0,
                    from include/uapi/linux/uuid.h:21,
                    from include/linux/uuid.h:19,
                    from include/linux/mod_devicetable.h:12,
                    from include/linux/pci.h:20,
                    from arch/powerpc/kernel/pci_32.c:6:
   arch/powerpc/include/asm/string.h:21:15: note: expected 'void *' but argument is of type 'const void *'
    extern void * memcpy(void *,const void *,__kernel_size_t);
                  ^~~~~~
   cc1: all warnings being treated as errors

vim +141 arch/powerpc/kernel/pci_32.c

e05b3b4a Paul Mackerras   2006-01-15  125  	 */
e05b3b4a Paul Mackerras   2006-01-15  126  	for (i=0; i<pci_bus_count; i++)
e05b3b4a Paul Mackerras   2006-01-15  127  		pci_to_OF_bus_map[i] = 0xff;
e05b3b4a Paul Mackerras   2006-01-15  128  
e05b3b4a Paul Mackerras   2006-01-15  129  	/* For each hose, we begin searching bridges */
a4c9e328 Kumar Gala       2007-06-27  130  	list_for_each_entry_safe(hose, tmp, &hose_list, list_node) {
44ef3390 Stephen Rothwell 2007-12-10  131  		struct device_node* node = hose->dn;
44ef3390 Stephen Rothwell 2007-12-10  132  
e05b3b4a Paul Mackerras   2006-01-15  133  		if (!node)
e05b3b4a Paul Mackerras   2006-01-15  134  			continue;
e05b3b4a Paul Mackerras   2006-01-15  135  		make_one_node_map(node, hose->first_busno);
e05b3b4a Paul Mackerras   2006-01-15  136  	}
8c8dc322 Stephen Rothwell 2007-04-24  137  	dn = of_find_node_by_path("/");
8c8dc322 Stephen Rothwell 2007-04-24  138  	map_prop = of_find_property(dn, "pci-OF-bus-map", NULL);
a7f67bdf Jeremy Kerr      2006-07-12  139  	if (map_prop) {
a7f67bdf Jeremy Kerr      2006-07-12  140  		BUG_ON(pci_bus_count > map_prop->length);
a7f67bdf Jeremy Kerr      2006-07-12 @141  		memcpy(map_prop->value, pci_to_OF_bus_map, pci_bus_count);
a7f67bdf Jeremy Kerr      2006-07-12  142  	}
8c8dc322 Stephen Rothwell 2007-04-24  143  	of_node_put(dn);
e05b3b4a Paul Mackerras   2006-01-15  144  #ifdef DEBUG
e05b3b4a Paul Mackerras   2006-01-15  145  	printk("PCI->OF bus map:\n");
e05b3b4a Paul Mackerras   2006-01-15  146  	for (i=0; i<pci_bus_count; i++) {
e05b3b4a Paul Mackerras   2006-01-15  147  		if (pci_to_OF_bus_map[i] == 0xff)
e05b3b4a Paul Mackerras   2006-01-15  148  			continue;
e05b3b4a Paul Mackerras   2006-01-15  149  		printk("%d -> %d\n", i, pci_to_OF_bus_map[i]);

:::::: The code at line 141 was first introduced by commit
:::::: a7f67bdf2c9f24509b8e81e0f35573b611987c80 [POWERPC] Constify & voidify get_property()

:::::: TO: Jeremy Kerr [off-list ref]
:::::: CC: Paul Mackerras [off-list ref]

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
-------------- next part --------------
A non-text attachment was scrubbed...
Name: .config.gz
Type: application/gzip
Size: 6114 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20170317/1359e19c/attachment.gz>